Patent Application
20080303734
The present invention relates to a dielectric leaky wave antenna, and in particular, to a dielectric leaky wave antenna with an excitation section and a radiation section, which uses a technology for making both characteristics of the excitation section and the radiation section possible to be optimized.
For example, there is a dielectric leaky wave antenna as an antenna with a simple configuration and a high efficiency, which is used in a quasi-millimeter waveband of 24.05 to 24.2 GHz assigned to Doppler radars.
In the dielectric leaky wave antenna 10, a dielectric image guide which transmits electromagnetic radiation in a direction perpendicular to a thickness direction of a dielectric substrate 11 is formed by the dielectric substrate 11 and a ground conductor 12 provided to one surface of the dielectric substrate 11 (the lower surface in the drawing). In addition, a plurality of metal strips for leakage 13 serving as a radiation section are provided at predetermined intervals in parallel to one another in a direction perpendicular to a transmission direction A of the electromagnetic radiation, at an opposite side (the upper surface in the drawing) of the dielectric substrate 11. Electromagnetic radiation to be fed from an excitation section 14 which will be described later is propagated in a direction perpendicular to the plurality of metal strips for leakage 13, whereby the electromagnetic radiation in the dielectric substrate 11 is made to leak from the surface of the dielectric substrate 11 to the exterior space.
Here, radiation characteristics of the electromagnetic radiation made to leak from the surface of the dielectric substrate 11 can be variously set in accordance with a width and an interval of the plurality of metal strips for leakage 13, and an angle between the wave front (the equiphase surface) of the electromagnetic radiation propagated in the dielectric substrate 11 and the plurality of metal strips for leakage 13.
For example, if the wave front of the electromagnetic radiation propagated in the dielectric substrate 11 is made to be parallel to the plurality of metal strips for leakage 13, a direction of beams of the electromagnetic radiation made to leak from the surface of the dielectric substrate 11 can be set in a plane which is perpendicular to the surface of the dielectric substrate 11 and perpendicular to the length direction of the plurality of metal strips for leakage 13.
Further, the direction of beams of the electromagnetic radiation in the plane is determined mainly on the basis of intervals among the plurality of metal strips for leakage 13.
For example, if the intervals among the plurality of metal strips for leakage 13 are set to be substantially the same as a propagating wavelength kg of electromagnetic radiation to be radiated in the dielectric image guide, a direction of beams of the electromagnetic radiation can be set to a direction substantially perpendicular to the surface of the dielectric substrate 11, which makes it possible to make an aspect of the dielectric substrate 11 and a direction of beams of the electromagnetic radiation substantially accord with each other.
In a dielectric leaky wave antenna which radiates electromagnetic radiation on the basis of such a principle, it is necessary to provide the excitation section 14 for propagating electromagnetic radiation having a wave front substantially parallel to the plurality of metal strips for leakage 13 in the dielectric substrate 11.
As the excitation section 14, one which can be configured with a simple configuration and high mass productivity at low cost has been proposed by the inventors in Pat. Document 1. As shown in
Note that, an arrow B in the excitation section 14 shown in
Pat. Document 1: Jpn. Pat. Appln. KOKAI Publication No. 2004-328291
However, when as descried above, a dielectric image guide for a radiation section and a microstrip line as an excitation section are formed on a common dielectric substrate 11, there is a new problem to be solved as follows.
Namely, in the dielectric image guide, the dielectric substrate 11 is required to have a given substrate thickness for confining an electromagnetic field. In contrast thereto, in the microstrip line, electromagnetic radiation leaks from the line itself when a substrate thickness is increased, and consequently, it is impossible to efficiently branch the electromagnetic radiation in a direction in which the plurality of metal strips for leakage 13 are provided.
Conventionally, the actual situation is such that a transmission characteristic of at least one of a dielectric image guide for a radiation section and a microstrip line as an excitation section is sacrificed.
An object of the present invention is, in order to solve the problem of the prior art as described above, to provide a dielectric leaky wave antenna which satisfies both of a transmission characteristic of a dielectric image guide for a radiation section and a transmission characteristic of a microstrip line for an excitation section, and which is made more efficient.
In order to achieve the above object, according to a first aspect of the present invention, there is provided a dielectric leaky wave antenna comprising:
a dielectric substrate (21);
a ground conductor (22) provided on one surface side of the dielectric substrate, the ground conductor forming a dielectric image guide which propagates electromagnetic radiation in a direction perpendicular to a thickness direction in the dielectric substrate;
a plurality of metal strips for leakage (23, 23′) provided in parallel to one another at predetermined intervals on an opposite surface side of the dielectric substrate; and
an excitation section (24) having a metal strip for guide (40) which forms a microstrip line between itself and the ground conductor and branching means (24A) for branching electromagnetic radiation transmitted in the microstrip line in a direction perpendicular to the plurality of metal strips for leakage in the dielectric substrate, wherein
the dielectric substrate is configured to have a lower layer portion (21a) and an upper layer portion (21b) joined on the lower layer portion,
the ground conductor is formed on a lower surface of the lower layer portion of the dielectric substrate,
the plurality of metal strips for leakage are formed on an upper surface of the upper layer portion of the dielectric substrate, and
the metal strip for guide and the branching means which configure the excitation section are formed between the lower layer portion and the upper layer portion of the dielectric substrate.
In order to achieve the above object, according to a second aspect of the present invention, there is provided the dielectric leaky wave antenna according to the first aspect, wherein
the branching means of the excitation section has:
a plurality of first stubs (41, 41′, 141) provided at predetermined intervals to an edge at one side of the metal strip for guide, the first stubs branching and outputting electromagnetic radiation, which is fed to the microstrip line and is propagated in a longitudinal direction of the microstrip line, in a direction perpendicular to the metal strips for leakage; and
a plurality of second stubs (51, 51′, 151) provided at predetermined intervals to an edge at the other side of the metal strip for guide, the second stubs branching and outputting electromagnetic radiation, which is fed to the microstrip line and is propagated in a longitudinal direction of the microstrip line, in a direction perpendicular to the metal strips for leakage, and
the predetermined intervals at which the plurality of first stubs and the plurality of second stubs are provided are equal to a guide wavelength of the electromagnetic radiation propagated in the microstrip line.
In order to achieve the above object, according to a third aspect of the present invention, there is provided the dielectric leaky wave antenna according to the second aspect, wherein
the plurality of first stubs and the plurality of second stubs are respectively provided such that corresponding stubs are shifted by substantially one fourth the guide wavelength of the electromagnetic radiation propagated in the microstrip line.
In order to achieve the above object, according to a fourth aspect of the present invention, there is provided the dielectric leaky wave antenna according to the second aspect, wherein
the plurality of first stubs and the plurality of second stubs are respectively provided at positions symmetric with respect to the metal strip for guide.
In order to achieve the above object, according to a fifth aspect of the present invention, there is provided the dielectric leaky wave antenna according to the fourth aspect, wherein
the branching means of the excitation section is provided with a plurality of reflex suppression elements respectively provided at positions symmetric with respect to the metal strip for guide at predetermined intervals respectively from the plurality of first stubs and the plurality of second stubs.
In order to achieve the above object, according to a sixth aspect of the present invention, there is provided the dielectric leaky wave antenna according to the second aspect, wherein
the plurality of first stubs and the plurality of second stubs are formed in band shapes extending by predetermined distances in a direction perpendicular to the metal strip for guide respectively with predetermined widths from the side edges of the metal strip for guide.
In order to achieve the above object, according to a seventh aspect of the present invention, there is provided the dielectric leaky wave antenna according to the fifth aspect, wherein
the plurality of reflex suppression elements are formed in band shapes extending by predetermined distances in a direction perpendicular to the metal strip for guide respectively with predetermined widths from the side edges of the metal strip for guide.
In order to achieve the above object, according to an eighth aspect of the present invention, there is provided the dielectric leaky wave antenna according to the first aspect, further comprising
a reflecting wall (70, 71) to reflect the electromagnetic radiation branched toward a side opposite to a side of the metal strips for leakage by the branching means, toward the side of the metal strips for leakage.
In order to achieve the above object, according to a ninth aspect of the present invention, there is provided the dielectric leaky wave antenna according to the first aspect, further comprising
a shield member (73, 74) having one end electrically connected to the ground conductor, and the other end extended so as to face the metal strip for guide at an opposite surface side of the dielectric substrate, the shield member shielding electromagnetic radiation directly radiated from the microstrip line to the opposite surface side of the dielectric substrate.
In order to achieve the above object, according to a tenth aspect of the present invention, there is provided the dielectric leaky wave antenna according to the first aspect, wherein
the excitation section is provided at a substantially central portion of the dielectric substrate, and the plurality of metal strips for leakage are respectively provided at both sides of the excitation section.
In order to achieve the above object, according to an eleventh aspect of the present invention, there is provided the dielectric leaky wave antenna according to the first aspect, wherein
the microstrip line is configured to propagate electromagnetic radiation fed from one end of the microstrip line to the other end of the microstrip line.
In order to achieve the above object, according to a twelfth aspect of the present invention, there is provided the dielectric leaky wave antenna according to the first aspect, wherein
the microstrip line is configured to propagate electromagnetic radiation fed from a substantially center of the microstrip line to both end sides of the microstrip line.
In order to achieve the above object, according to a thirteenth aspect of the present invention, there is provided the dielectric leaky wave antenna according to the first aspect, wherein
a circuit board (110) is provided at an opposite side of the dielectric substrate with respect to the ground conductor, and an electrode section (111) of the circuit board and a part of the metal strip for guide are connected via a slot (22a) formed in the ground conductor.
In order to achieve the above object, according to a fourteenth aspect of the present invention, there is provided the dielectric leaky wave antenna according to the first aspect, wherein
a circuit board (110) is provided at an opposite side of the dielectric substrate with respect to the ground conductor, and an electrode section (111) of the circuit board and a part of the metal strip for guide are connected via a metal pin (112) formed so as to penetrate through the lower layer portion of the dielectric substrate, the ground conductor, and the circuit board.
In order to achieve the above object, according to a fifteenth aspect of the present invention, there is provided the dielectric leaky wave antenna according to the first aspect, wherein
the metal strip for guide and the branching means which configure the excitation section are formed by a print process on an upper surface of the lower layer portion or a lower surface of the upper layer portion of the dielectric substrate.
In the dielectric leaky wave antenna of the invention configured as described above, the metal strip for guide of the excitation section is formed between a lower layer portion and an upper layer portion of the dielectric substrate. As a consequence, a thickness of the microstrip line for an excitation section can be freely set with respect to a thickness of the entire dielectric substrate required for the dielectric image guide for transmitting electromagnetic radiation to the side of the metal strips for leakage. For this reason, an attempt can be made to optimize characteristics of the dielectric image guide and the microstrip line, and an attempt can be made to make the dielectric leaky wave antenna more efficient without sacrificing both the characteristics of the guide and the line.
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, the brief summary of the present invention will be described. In the invention, as shown in
These are respectively used for first, second, third, fourth, fifth, and sixth embodiments (which will be described later) to which a dielectric leaky wave antenna according to the invention is applied, and modified examples of the excitation sections in these embodiments.
Further, examples of the embodiments of radiation sections including a plurality of metal strips for leakage 23 arranged on one side of the excitation sections are shown in
These are respectively used for the first, second, third, fourth, fifth, and sixth embodiments (which will be described later) to which the dielectric leaky wave antenna according to the invention is applied.
Moreover, examples of the embodiments of radiation sections including a plurality of metal strips for leakage 23 arranged on the both sides of the excitation sections are shown in
These are respectively used for the first, second, third, fourth, fifth, sixth, and seventh embodiments (which will be described later) to which the dielectric leaky wave antenna according to the invention is applied.
Here, the seventh embodiment shown in
Note that an aspect according to the first embodiment described with reference to
Namely,
Further,
The dielectric leaky wave antenna 20 basically includes: a dielectric substrate 21; a ground conductor 22 provided to one surface side of the dielectric substrate, the ground conductor 22 forming a dielectric image guide which propagates electromagnetic radiation in a direction perpendicular to a thickness direction in the dielectric substrate; a plurality of metal strips for leakage 23 provided in parallel to one another at predetermined intervals at an opposite surface side of the dielectric substrate 21; and an excitation section 24 having a metal strip for guide 40 which forms a microstrip line between itself and the ground conductor 22, and branching means 24A for branching electromagnetic radiation transmitted in the microstrip line in a direction perpendicular to the plurality of metal strips for leakage 23 in the dielectric substrate. The dielectric substrate 21 is configured to have a lower layer portion 21a and an upper layer portion 21b joined onto the upper surface of the lower layer portion 21a, and the ground conductor 22 is formed on the lower surface of the lower layer portion 21a of the dielectric substrate 21. The plurality of metal strips for leakage 23 are formed on the upper surface of the upper layer portion 21b of the dielectric substrate 21. The metal strip for guide 40 and the branching means 24A which configure the excitation section 24 are formed between the lower layer portion 21a and the upper layer portion 21b of the dielectric substrate 21.
Specifically, the dielectric leaky wave antenna 20 is, for example, an antenna which covers a 24.05 to 24.2 GHz frequency band for use in Doppler radars or the like within a quasi-millimeter waveband.
In the dielectric leaky wave antenna 20, as described above, a dielectric image guide which allows electromagnetic radiation to be propagated in a direction of the arrows A perpendicular to the thickness direction in the dielectric substrate 21 is formed by the dielectric substrate 21 and the ground conductor 22 provided to be joined so as to overlap onto one surface side (the lower surface side) of the dielectric substrate 21 with no space.
Further, the plurality of metal strips for leakage 23 are provided at predetermined intervals, for example, at intervals which are substantially equal to a guide wavelength λg of electromagnetic radiation propagated in the dielectric image guide, onto the opposite surface side (the upper surface side) of the dielectric substrate 21.
Note that the ground conductor 22 and the plurality of metal strips for leakage 23 are formed by a print process or etching process of a metal film onto the dielectric substrate 21.
The dielectric substrate 21 is made of alumina, ceramic, various types of resins, or the like, and has a structure of at least two layers in which the lower layer portion 21a and the upper layer portion 21b are overlapped with each other to be joined together.
Dielectric materials of identical material are generally used as the lower layer portion 21a and upper layer portion 21b. However, different types of materials may be also used.
The plurality of metal strips for leakage 23 formed on the surface of the upper layer portion 21b of the dielectric substrate 21 are respectively composed of two metal strips 23a and 23b separated by substantially one fourth the guide wavelength kg in parallel to each other in order to suppress reflective components generated in the dielectric image guide.
In this case, when the plurality of metal strips for leakage 23 are composed of only the metal strips 23a at intervals substantially equal to the guide wavelength λg, reflected waves generated by the metal strips 23a are made to be in phase, which degrades the radiant efficiency as an antenna.
However, the metal strips 23b in the same size as the metal strips 23a are respectively provided at positions separated by substantially one fourth the guide wavelength λg from the metal strips 23a as described above. As a consequence, reflected waves from the both are made to have phases reversed each other, which makes it possible to set off the reflective components. Therefore, it is possible to suppress deterioration in the radiant efficiency as an antenna.
The metal strips 23a and 23b each have a function of leaking electromagnetic radiation. For this reason, when each of the plurality of metal strips for leakage 23 is constituted by the two metal strips 23a and 23b as described above, the radiant efficiency of electromagnetic radiation leaked from the surface of the dielectric substrate 21 is made to be radiant efficiency in which radiant efficiencies of electromagnetic radiation respectively made to leak by the two metal strips 23a and 23b are synthesized.
In this embodiment and all embodiments which will be shown hereinafter, each of the plurality of metal strips for leakage 23 is constituted by the two metal strips 23a and 23b.
However, the invention is not limited thereto. When reflective components by the metal strips are little enough to be ignored, each metal strip for leakage 23 may be composed of one metal strip.
In addition, it is possible to suppress reflected waves by setting the intervals among the plurality of metal strips for leakage 23 to be shorter or longer than the guide wavelength kg. Consequently, even in such a case, each of the plurality of metal strips for leakage 23 can be constituted by one metal strip.
On the other hand, the excitation section 24 is formed at a position separated from the plurality of metal strips for leakage 23, and in the inside at one end side of the dielectric substrate 21 to the left in the drawing, i.e., between the lower layer portion 21a and the upper layer portion 21b of the dielectric substrate 21.
The excitation section 24 is composed of the metal strip for guide 40 which extends in a band shape in parallel to the plurality of metal strips for leakage 23, the metal strip for guide forming a microstrip line between itself and the ground conductor 22, a plurality of (four simply shown in
The metal strip for guide 40 and the respective stubs 41 and 51 which configure the excitation section 24 are formed by a print process or etching process of a metal film onto the upper surface side of the lower layer portion 21a or the lower surface side of the upper layer portion 21b before the dielectric substrate 21 is formed in such a manner that the lower layer portion 21a and the upper layer portion 21b are overlapped with each other to be joined together.
Here, the metal strip for guide 40 forms a microstrip line with the lower layer portion 21a of the dielectric substrate 21 between itself and the ground conductor 22, which propagates electromagnetic radiation fed from the edge with an electric field in the direction of arrow B from a feed point 25 at the one end side to the other end side in the direction of arrow C.
Then, the respective stubs 41 and 51 function as the branching means 24A for branching the electromagnetic radiation propagated from the one end side to the other end side of the microstrip line in the direction of arrows A in which the metal strips for leakage 23 are provided in the dielectric substrate 21.
Note that a method for supplying electromagnetic radiation to the feed point 25 will be described later.
A transmission characteristic of the excitation section 24 can be arbitrarily set in accordance with a width of the metal strip for guide 40, widths, lengths, and intervals, etc. of the respective stubs 41 and 51.
Namely, as shown in the left of
Further, because phases of the excitation waves branched to be output from the respective stubs depend on an interval Q between stubs, it is possible to arbitrarily set a phase characteristic of the entire excitation waves in accordance with an interval between the stubs.
For example, when the interval Q is set to an integer multiple of a guide wavelength λg′ (Q=λg′), phases of the excitation waves respectively branched to be output from the first stubs 411 to 414 portions are made equal to one another, and a phase front of the entire excitation waves is made parallel to the metal strip for guide 40 as Ph1-Ph1′ shown in the right of
Assume that, in this way, such excitation waves with the phase front Ph1-Ph1′ which is parallel to the metal strip for guide 40 are propagated to the side of the plurality of metal strips for leakage 23 which are parallel to the metal strip for guide 40. In this case, it is possible to radiate electromagnetic radiation whose central beam direction is perpendicular to the surface of the dielectric substrate 21, and which is located on a plane perpendicular to the metal strip for guide 40, from the surface of the dielectric substrate 21.
Further, when the interval Q is set to be shorter than an integer multiple of the guide wavelength λg′ (Q<λg′), phases of the excitation waves respectively branched to be output from the first stubs 411 to 414 portions are made to gradually advance, and a phase front of the entire excitation waves is slightly inclined toward the metal strip for guide 40 as Ph2-Ph2′ shown in the right of
In this way, the excitation waves with the phase fronts Ph2-Ph2′ and Ph3-Ph3′ inclined toward the metal strip for guide 40 are propagated toward the side of the plurality of metal strips for leakage 23 which are parallel to the metal strip for guide 40. As a result, it is possible to radiate electromagnetic radiation whose central beam direction is inclined toward the feeding end side or the terminal end side from the surface of the dielectric substrate 21.
Namely, as one specific configuration example, as shown in
Note that in some cases, the excitation section 24 having the configuration shown in
The interval Q among the first stubs 411 to 414 is set to a value approximate an integer multiple of the wave length λg′ in the microstrip line (metal strip for guide) of electromagnetic radiation to be radiated. Thus, the electromagnetic radiation, which is fed by the feed point 25 to be propagated from the one end side to the other end side of the microstrip line, is branched to be output as excitation waves in the direction of arrows A (refer to
Further, in the same manner as in the case of the two metal strips 23a and 23b of each of the plurality of metal strips for leakage 23 described above, the second stubs 511 to 514 are to set off the reflective components by generating reflective components with reversed phases of the reflective components generated by the first stubs 411 to 414. The second stubs 511 to 514 are respectively provided at positions separated by one fourth the guide wavelength λg′ of the electromagnetic radiation propagated in the microstrip line from the first stubs 411 to 414.
More specifically, as another configuration example in place of the excitation section 24 having alternate stubs according to the first embodiment described above, the respective elements of the first stubs 411 to 414 and the respective elements of the second stubs 511 to 514 corresponding to the first stubs 411 to 414 are, as shown in
With such an arrangement, electric currents opposite to each other are made to respectively flow in the elements of the first stubs 411 to 414 and the elements of the corresponding second stubs 511 to 514, and therefore, radio wave is not radiated from these stub elements to the upper surface of the dielectric substrate 21.
Accordingly, because radio wave radiation to the upper surface of the dielectric substrate 21 is not brought about, the electromagnetic radiation transmitted in the microstrip line is efficiently branched to be output as excitation waves in a direction in which the plurality of metal strips for leakage 23 are provided in the dielectric substrate 21.
However, in the configuration of
In particular, when an interval among the respective stubs 41 and 51 is substantially equal to the wavelength of the electromagnetic radiation propagated in the microstrip line, reflection from the respective stub elements returns to the feed point 25 so as to be in plane, which becomes great reflection, and the radiant efficiency as an antenna is degraded.
Note that in some cases, the excitation section 24 having the configuration shown in
Namely, the third embodiment is provided as a configuration example in place of the excitation section 24 having alternate stubs according to the first embodiment described above. That is, as shown in
In this way, if the reflex suppression elements 611 to 614 and 711 to 714 are arranged at predetermined intervals δ from the elements of the first stubs 411 to 414 and the elements of the second stubs 511 to 514, it is possible to reduce occurrence of reflection which is problematic in the second embodiment.
Note that the predetermined intervals δ at which the reflex suppression (stub) elements 611 to 614 and 711 to 714 are arranged from the elements of the first stubs 411 to 414 and the elements of the second stubs 511 to 514 are, for example, a value of about ½ the guide wavelength λg′, and an appropriate value is experimentally found.
As is clear from
Note that in some cases, the excitation section 24 having the configuration shown in
With respect to the dielectric leaky wave antenna 20 according to the first to third embodiments configured as described above, the dielectric substrate 21 is made to have a structure of at least two layers, which is a structure in which the metal strip for guide 40 configuring a microstrip line of the excitation section 24 is provided in the inside of the dielectric substrate 21. For this reason, an attempt can be made to respectively optimize the dielectric image guide for leakage and the microstrip line for excitation without sacrificing transmission characteristics of the both.
Namely, a thickness of the entire dielectric substrate 21 is set to a thickness t which is necessary and sufficient for confining an electromagnetic field in the dielectric image guide for leakage, and it suffices to set a thickness or the like within the entire thickness t such that the transmission characteristic of the microstrip line for excitation is made favorable.
Note that the electric field distributions are characteristics of the metal strip for guide 40 itself determined by omitting the stubs 41 and 51.
It is clear that, in the electric field distributions of the dielectric leaky wave antenna with the conventional structure, great turbulence is brought about in a region near the feed point, and a loss (inclination) varies overall.
These turbulence and variation show that the electromagnetic radiation leaks from the microstrip line itself in the vicinity of the feed point because the dielectric substrate is too thick.
In contrast thereto, it is clear that, in the electric field distributions of the dielectric leaky wave antenna 20 of the invention shown in
Namely, a surface side of a metal strip for guide is opened in a general microstrip line, while the microstrip line in the respective embodiments described above is covered with dielectric.
However, as shown in
This electric field distribution is reduced at a substantially constant slope, and a quantity of the reduction is output as an excitation wave.
Accordingly, it is found that the excitation section 24 is formed in the inside of the dielectric substrate 21, whereby it is possible to output uniform excitation waves to the side of the plurality of metal strips for leakage 23.
As described above, it is clear that a thickness of the dielectric substrate 21 cannot be made too thick with respect to the metal strip for guide 40.
In contrast thereto, a thickness of the dielectric substrate 21 cannot be made too thin with respect to the plurality of metal strips for leakage 23.
More specifically, it is clear from
Then, when the width of each metal strip for leakage 23a is made to be approximate 2.5 mm, a leakage quantity is increased. However, not only a leakage quantity is still little, but also an interval with the other metal strip for leakage 23b serving as a reflex suppression element is made extremely narrow in accordance with the width.
Therefore, joints between the metal strips for leakage 23a and the other side metal strips for leakage 23b are made large, which disturbs the electric field distribution. As a result, an effect of suppressing reflection is lost.
Namely, it is found that the thickness of the dielectric substrate 21 with respect to the respective metal strips for leakage 23 must be made thicker than the thickness of the dielectric substrate 21 with respect to the microstrip line of the excitation section 24.
According to the invention, it is possible to realize a high-performance dielectric leaky wave antenna by providing thicknesses which are optimum for both of the respective metal strips for leakage 23 and the microstrip line for excitation as the thickness of the dielectric substrate 21.
Here, description has been given to an example in which the metal strip for guide 40 is provided so as to be parallel to the plurality of metal strips for leakage 23.
However, the metal strip for guide 40 may be at a slope toward the plurality of metal strips for leakage 23.
In this way, the excitation section 24 of the dielectric leaky wave antenna 20 in the respective embodiments described above has the metal strip for guide 40, the plurality of first stubs 41 and the reflex suppression second stubs 51. The metal strip for guide 40 is separated from the plurality of metal strips for leakage 23 on the surface of the dielectric substrate 21, is provided between the lower layer portion 21a and the upper layer portion 21b of the dielectric substrate 21, and forms a microstrip line between itself and the ground conductor 2. The first stubs 41 and reflex suppression second stubs 51 are provided at predetermined intervals at the side edges of the metal strip for guide 40, and branch and output electromagnetic radiation fed into the microstrip line in a direction perpendicular to the plurality of metal strips for leakage 23.
Consequently, the excitation section 24 can be integrated with the dielectric substrate 21, and the entire antenna can be downsized.
Further, the dielectric substrate 21 is formed such that the lower layer portion 21a and the upper layer portion 21b are overlapped to be joined together, and the excitation section 24 composed of the metal strip for guide 40 and the respective stubs 41 and 51 is formed between the lower layer portion 21a and the upper layer portion 21b. For this reason, it is possible to freely set a thickness of the microstrip line for excitation with respect to an entire thickness of the dielectric substrate 21 necessary for the dielectric image guide for transmitting electromagnetic radiation toward the side of the plurality of metal strips for leakage 23. Thus, an attempt can be made to optimize the transmission characteristics of the guides, and it is possible to make radiation as the entire antenna highly efficient without sacrificing the characteristics of the both guides.
As described above, even when the excitation section 24 is formed in the inside of the dielectric substrate 21, it suffices to form the metal strip for guide 40 and the respective stubs 41 and 51 by a print process or etching process at the upper surface side of the lower layer portion 21a or the lower surface side of the upper layer portion 21b before the lower layer portion 21a and the upper layer portion 21b are overlapped to be joined together. Consequently, the antennas can be manufactured at low cost and easily with fewer processes, which makes it possible to produce such antennas in large quantities.
Such a manufacturing process can be achieved easily by using a multilayer printed board technology.
When, in the dielectric leaky wave antenna 20 with the above-described configuration, the components of the excitation wave branched toward a side opposite to the side at which the plurality of metal strips for leakage 23 are provided are great enough not to be ignored, it is necessary to allow the excitation wave branched toward the opposite side to be reflected to the side at which the metal strips for leakage 23 are provided.
In this case, an end face 21c of the dielectric substrate 21 on the side at which the metal strip for guide 40 is provided can be utilized as a reflecting wall if the dielectric substrate 21 with a great relative permittivity such as ceramic or alumina is used.
At that time, it suffices to set distances from the position of the reflecting wall to the metal strip for guide 40 and the plurality of metal strips for leakage 23 such that phases of reflected waves which reflect from the end face 21c of the dielectric substrate 21, and go toward the side at which the plurality of metal strips for leakage 23 are provided, and of excitation waves which go directly toward the side at which the plurality of metal strips for leakage 23 are provided from the metal strip for guide 40, accord with one another.
In addition, when the dielectric substrate 21 with a little relative permittivity such as Teflon (registered trademark) as resin fluoride is used, electromagnetic radiation is radiated from the end face, which may greatly degrade the radiant efficiency as the entire antenna.
In such a case, as shown in
Note that, when the reflective member 70 is formed by printing, an auxiliary member 70a is formed in a pattern on the surface of the dielectric substrate 21 (the upper surface of the upper layer 21b) as shown in
That is,
Further,
Moreover, instead of providing the reflective member 70 on the end face as described above, as shown in
Namely,
Further,
Note that, in
However, such a short-circuiting member 71a is not necessarily required, and can be omitted in some cases.
Also when the reflective member 70 and the metal pins 71 are used, in the same manner as described above, positions of the respective portions are set such that phases of reflected waves which reflect from the end face 21c of the dielectric substrate 21, and go toward the side at which the plurality of metal strips for leakage 23 are provided, and excitation waves which go directly toward the side at which the plurality of metal strips for leakage 23 are provided from the metal strip for guide 40 accord with one another.
Further, even when the excitation section is provided in the inside of the excitation section dielectric substrate 21 in the antenna having an edge feeding system shown in
In the case where the effect by the direct radiant characteristic cannot be ignored, it suffices, as shown in
Namely,
Further,
Further, as a dielectric leaky wave antenna 80 shown in
Namely,
However, because a phase difference is generated in the respective electromagnetic radiation branched to right and left, it is necessary to adjust distances d and d′ from the metal strip for guide 40 to the first right-and-left metal strips for leakage 23 and 23′.
More specifically, in the case of
Further, in the case of
The dielectric leaky wave antenna 20 according to the first to third embodiments and the modified example thereof have been shown in the cases of the edge feeding system in which electromagnetic radiation is supplied from the feed point 25 at the one end side of the microstrip line.
However, as shown in
Also in the case of such a center feeding system, it is possible to control the distribution of the electromagnetic radiation branched to be output into the dielectric substrate 21 by setting widths and lengths of the stubs 41 and 51 in the excitation sections 24 appropriately.
In
In this case, as shown in the left of
In this case, each of the second stubs 511 to 513 and second stubs 511′ to 513′ functions for reflex suppression in the same manner as described above.
For example, when stub intervals Q and Q′ are set to be equal to an integer multiple of the guide wavelength λg′ (Q=Q′=λg′), a phase front Ph1-Ph1′ which is parallel to the metal strip for guide 40 is obtained as shown in the right of
Further, when the stub interval Q is set to be shorter than an integer multiple of the guide wavelength λg′, and the stub interval Q′ is set to be longer than an integer multiple of the guide wavelength λg′ (Q<λg′<Q′), a phase front Ph2-Ph2′ which is slightly inclined toward the metal strip for guide 40 is obtained.
In contrast thereto, when the stub interval Q is set to be longer than an integer multiple of the guide wavelength λg′, and the stub interval Q′ is set to be shorter than an integer multiple of the guide wavelength λg′, (Q>λg′>Q′), a phase front Ph3-Ph3′ which is slightly inclined in the opposite direction of the phase front Ph2-Ph2′ toward the metal strip for guide 40 is obtained.
In
In the case of such a center feeding system, a loss (a conductor loss or a dielectric loss) occurring in the guide is made to be substantially half when a length of the microstrip line is the same as that in the edge feeding described above, so that the performance as the antenna is enhanced.
Further, even when there are manufacturing errors or the like in the case where the phase front Ph1-Ph1′ parallel to the metal strip for guide 40 is obtained, the phase front Ph1-Ph1′ is inclined symmetrically as the phase front Ph4-Ph4′ shown in the right of
In
In
In
In
In
In
More specifically, in the respective dielectric leaky wave antennas described above, the metal strips for leakage 23 and 23′ and the metal strip for guide 40 are formed so as to be substantially parallel to one side of the rectangular dielectric substrate 21.
However, the present invention is not limited thereto, and orientations of the metal strips for leakage 23 and 23′ and the metal strip for guide 40 with respect to the shape of the dielectric substrate 21 can be arbitrarily set.
For example, as shown in
In this case, if electromagnetic radiation with a phase front parallel to the metal strips for leakage 23 and 23′ at the both sides is propagated from the excitation section 24, it is possible to allow electromagnetic radiation with polarization perpendicular to the length direction to leak from the metal strips for leakage 23 and 23′.
A direction of the polarization of the electromagnetic radiation is made to be 45° polarization which is inclined at 45° on the basis of one side of the rectangular dielectric substrate 21, which is suitable for a automobile radar or the like.
(Modified Examples of Excitation Section)
Namely, in the respective embodiments described above, the stubs 41 and 51 projected from the side edges of the metal strip for guide 40 are used as the branching means 24A for branching and outputting electromagnetic radiation propagated in the microstrip line constituted by the metal strip for guide 40 and the ground conductor 22 toward the side of the metal strips for leakage 23.
However, the present invention is not limited thereto, as shown in
In other words, not only the stubs as described above, as shown in
In this example, branching means is provided to the metal strip for guide 40′ itself. The invention is not limited to the above-described example, and branching means can be achieved by periodically perturbing to the metal strip for guide.
(Embodiment of Feed Unit)
In the dielectric leaky wave antennas 20 and 80 in the respective embodiments described above, description of the configuration itself of the feed point 25 of the excitation section 24 formed in the dielectric substrate 21, i.e., of the feed unit has been omitted.
However, with respect to the structure of the feed unit, feeding can be carried out via a slot or a metal pin formed by through-hole plating or the like from the lower surface side of the ground conductor 22.
For example, in the case of edge feeding, the configuration is made as shown in
Further, in the case of center feeding, the configuration is made as shown in
Namely, as shown in
In accordance with the present invention as described above, it is possible to provide a dielectric leaky wave antenna improved in efficiency which solves the problem in the prior art as described above, and which satisfies both of a transmission characteristic of a dielectric image guide for a radiation section, and a transmission characteristic of a microstrip line for an excitation section.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-214214 | Jul 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP06/14421 | 7/20/2006 | WO | 00 | 1/3/2007 |
